Evidence for Ocean Found at Saturn's Moon Titan

This image shows bodies of liquid near Titan's north pole. It show that many of the features commonly associated with lakes on Earth, such as islands, bays, inlets and channels, are also present on this cold Saturnian moon.Credit: NASA/JPL

An
ocean seasoned with the chemical ingredients of life may lie hidden beneath the
icy surface of Saturn's moon Titan.

The
evidence? The entire surface of Titan appears to be sliding around, scientists
say, like cheese over tomato sauce on a slice of pizza.

Titan
is the largest of the more than 50 known moons orbiting Saturn, and is in fact bigger than the
planet Mercury. Titan possesses a thick, planet-like atmosphere ? the only moon
in the solar system known to have one. And the Cassini-Huygens mission to
Saturn and its moons revealed a surface at Titan covered with icy mountains,
oily lakes and seas and what might be "cryovolcanoes" that spew
plumes of water and ammonia.

Scientists
had long suspected that an underground
ocean might exist on Titan, much as Jupiter's moons Ganymede, Callisto and
Europa do.

"Models
of heat flow in Titan's interior suggested years ago that Titan would likely
have an internal water or water-ammonia ocean," said Ralph Lorenz, a Cassini radar team
member at the Johns Hopkins University Applied Physics Lab in Laurel, Md.

Lorenz and his colleagues
analyzed several years' worth of radar data from the Cassini-Huygens
mission. They found evidence that some features on the moon's surface had
drifted.

"As
we were mapping Titan's surface, we were building maps up in little strips.
Some of these strips overlapped, help tying the map together, but when you
looked at where the features were in one strip compared with another strip, the
coordinates weren't the same," Lorenz explained.

Their
research suggests that winds in Titan's dense atmosphere might actually rock
the moon back and forth on its axis, influencing how it spins. The winds can
accelerate the small moon's rotation speed and then, as the winds change with
the seasons, they can decelerate it.

"Titan's
winds should spool up and spin down with the seasons, and because Titan's
atmosphere is so massive and Titan is relatively small, the winds have a
measurable impact on Titan's rotation," Lorenz said. "If you adjust the
parameters of how Titan rotates very slightly, we could make the features on
the maps match up."

Winds
actually sway the rotation of Earth too, changing the length of the day by
roughly 1 millisecond over the course of the year. "But Titan's
atmosphere is so massive and its crust is light, so the changes are much bigger
there," Lorenz explained.

The
size of these shifts hints that Titan's crust and core have to be separated by
a liquid ocean to allow the atmosphere to move the crust around. Titan is about 3,200
miles (5,150 km) in diameter. The hidden ocean may be 60 to 120 miles (100 to
200 km) thick and its ice crust may be 30 to 90 miles (50 to 150 km) thick,
Lorenz said. Beneath that may be a few hundred miles of a heavier form of ice
"that you get at higher pressures," he explained, on top of a rocky
core roughly 1,800 to 2,100 miles (3,000 km to 3,400 km) wide.

This
underground ocean is likely mostly water with a dash of ammonia. As organic
molecules ? the chemical ingredients of life on Earth ? have been detected on
Titan's surface, it may be they are in the ocean as well.

"Whether
life has ever evolved on Titan is another question, but whether it did or
didn't, Titan can tell us about the chemical processes that ultimately lead to
life," Lorenz told SPACE.com.

Cassini
may make magnetic and gravity measurements that show more evidence of an ocean,
"but in the future it would be ideal to put a long-lived lander on Titan
with a seismometer to detect the ocean that way," Lorenz said. "ESA
and NASA are right now evaluating such a mission for launch in the 2017
timeframe."

However,
there might be another explanation other than a hidden ocean behind these
findings. Titan might have a reoccurring wobble in its orbit, said NASA Jet Propulsion
Laboratory planetologist Christophe Sotin, who did not participate in this study. To
confirm if Titan has an underground sea or not, Sotin said, Cassini would need
to observe that moon for another six years to see if its spin slows down, as
would be expected if there was a subterranean ocean.

"If
there is the presence of an ocean there, with a pressure and temperature very
similar to Earth's oceans, the question of life is now open for Titan,"
Sotin said.

Lorenz
and his colleagues detail their findings in the March 21 issue of the journal Science.